There is clear evidence that Earth's surface temperature has risen by about 0.5°C over the last 100 years. However, there is some uncertainty as to the
causes of this temperature increase, as well as what its short- and
long-term effects will be on regional and global scales. Predictive
computer models indicate that given a steady rise in levels of greenhouse
gases, such as carbon dioxide, there will be a corresponding increase in
surface temperatures. Yet surprisingly, despite a 30 percent increase in
carbon dioxide levels since the beginning of the Industrial Revolution,
temperatures haven't risen as much as the models predicted. Why? Because
greenhouse gases aren't the only influence on temperature. There are many
other variables--such clouds, aerosols, and the ocean--that also affect
temperature.

Air and sea embrace

The Earth's ocean and atmosphere are locked in such an intricate
embrace--as one changes so changes the other. At the interface between air
and sea, there is a constant flow of information, as vast amounts of energy
and chemicals (in the form of gases and aerosols) are continually being
exchanged. If energy and chemicals are the languages that program the
behavior of atmosphere and ocean, then regional and global scale climate
variations are the outputs from this complex system. If scientists could
learn to better interpret the "dialogue" between ocean and atmosphere, they
could do a better job of predicting regional and global climate change.

Since the 1960s, scientists have developed sophisticated computer models to
help them understand the ocean's role in moderating climate. Yet many
questions remain unanswered. In recent decades, the ocean has partially
offset the anticipated global warming due to rising greenhouse gas levels
by exerting a cooling effect on climate. But, over the long run,
scientists don't know whether the ocean's cooling influence will persist.
Some theorize that if the ocean's circulation system changes, then the
ocean could contribute to, or even amplify, global warming. At the heart
of global-scale oceanography are the following questions: How will global
warming affect life in the ocean? How do ocean temperature, chemistry, and
biology influence climate? Are human activities contributing to changes in
the marine environment and, in turn, how might these changes feed back to
affect us?

Reliable sea surface temperature measurements from space-based sensors have
been a goal of oceanographers since the late 1960s. For the first time
ever, NASA's Earth Observing System (EOS) missions will provide
oceanographers with the radiometric resolution and precision, the
scientific calibration, the surface viewing geometry, and the ability to
remove atmospheric effects (such as clouds and aerosols) that will enable
measurements of sea surface temperature accurate to within 0.5 Kelvin.
These data will enable a better understanding of physical ocean-atmosphere
coupling--particularly during El Niño events.

Moreover, by precisely measuring ocean color, scientists can accurately
estimate the concentrations of phytoplankton on a global scale. Coupling
ocean color measurements with atmospheric aerosol and trace gas
measurements will also yield new insights into the chemical links between
ocean and atmosphere.

The SeaStar spacecraft, developed by OSC, carries the Sea-viewing
Wide-Field-of -view Sensor (SeaWiFS). SeaStar was launched on August 1,
1997, into a low Earth orbit. SeaWiFS is specially designed to precisely
measure ocean color, allowing scientists to monitor the abundance and
distribution of phytoplankton, as well as ocean currents. (Courtesy of the
SeaWiFS Project)